1. Field of Invention
This invention relates to a circuit test device which switches between a DC characteristic test and a function test of a test object without using a relay.
2. Description of the Prior Art
In testing a circuit, such as one comprising an integrated circuit or semiconductors, one may use a direct current characteristic test (hereinafter called "DC Test"). Another test is the function test, wherein the function of the circuit is tested (called "Function Test").
The DC Test is a test of the input or output of the test object (hereinafter called "DUT") and the power source system used therewith. Generally, there are two types of DC Tests; one test type is called the VSIM (V source I measure) for measuring a current when a pre-determined voltage is applied to the DUT; the other type is called the ISVM (I source V measure) for measuring a voltage when a predetermined current is applied to the DUT.
The Function Test is a test for deciding whether the DUT is favorable or not (i.e. Operationally suitable or not) by applying a clock signal and an input pattern to the input of the DUT to compare the output of the DUT with an expected pattern.
The operation of the circuit test using the conventional circuit test device will now be discussed. This conventional circuit is described in the Silver Series No. 8, LSI Testing Technology, p 189, Published Dec. 25, 1986 by Tricupps Co., Ltd.
FIG. 1 shows the pin electronics of a conventional circuit test device, wherein a DC test is performed by releasing relays RL1 and RL2 and connecting relays RL3 and RL4 so that a DUT 1 is connected to the DC measuring circuit. When a signal is outputted to the DUT by releasing relays RL3 and RL4 and connecting relays RL1 and RL2, the input pattern is converted into a high level pulse waveform V.sub.IH and a low level pulse waveform V.sub.IL by a driver 2. The waveforms are outputted to DUT 1. Where a signal is inputted from DUT 1, the output waveforms of DUT 1 are compared, in level, with a high comparative voltage V.sub.OH and a low comparative voltage V.sub.OL, respectively, by comparators 3 and 4. A decision circuit 5 compares the results of level comparison with an expected pattern at the timing of a strobe signal, to determine whether the DUT 1 is favorable or not. In this case, an I/O signal is determined depending on whether the pin electronics is an output signal or an input signal. In other words, driver 2 is controlled in three stages with the I/O signal. In addition, a MASK signal refers to a signal which does not require a decision by decision circuit 5.
In order to eliminate the effect of the structure of the DC Test on a Function Test, switching between the DC Test and the Function Test has been peformed by a relay. However, in recent years, miniaturization of test devices has become the norm, and when a relay is used in such devices, the following problems arise. Namely, when the relay is provided on pin electronics, an IC cannot be used in the pin electronics in a miniaturized test device. Also, pin electronics requires a large number of pins amounting to as many as 256 or 512 pins. Accordingly, the number of relays becomes large and miniaturization of test devices utilizing such numbers of relays is hindered. Also, the use of relays reduces reliability of such test circuit devices.